The development of smaller circuits having improved specifications have been investigated to a certain extent. In some applications, it was found useful to use photonic integrated circuits (PICs), i.e. devices that involve the use of light directly on a photonic chip in a manner analogous to the use of electricity in electronic chips.
These PICs are generally configured to process light and to propagate it from photonic device to photonic device via PIC waveguide elements present on the photonic chip. In some PICs, the light emitted from the exit end of an external waveguide element is coupled to one of the PIC waveguide elements of the PICs. This optical coupling typically involves precise alignment of the external waveguide element relative to the PIC waveguide element in order to achieve an acceptable coupling efficiency, which can be defined as the fraction of the light exiting from the external waveguide element that is coupled and then guided in the PIC waveguide element. Since the external waveguide element, the PIC waveguide elements and the other components required in the optical coupling schemes are manufactured and positioned with finite tolerances, the precise alignment needed for obtaining the acceptable coupling efficiency can be difficult to achieve.
Although the existing optical coupling techniques are found to be satisfactory to a certain extent, there remains room for improvement, especially in terms of improving the coupling efficiency, of relaxing the requirements on the alignment of the external waveguide element relative to one of the PIC waveguide element of the PIC and of compensating for misalignments due to the finite manufacturing tolerances of the components and post-assembly relative displacements of those components.